Field plate trench transistors are known semiconductor components and have a cell array, in which a plurality of trenches are provided. The trenches are separated from one another by mesa regions (semiconductor regions that enclose the trenches or adjoin the trenches). Source, body and drift regions are provided in the mesa regions.
Two electrodes are usually formed in field plate trench transistors: in a lower region of the trench, a field electrode (“field plate”) is provided, which is electrically insulated from the inner walls of the trench by means of an insulation layer (e.g. a field oxide layer). In an upper region of the trench, a gate electrode is provided, which is electrically insulated from the inner walls of the trench by means of one or more insulation layers (e.g. by means of two mutually opposite gate oxide layers). The field electrode is preferably electrically insulated from the gate electrode (for example by parts of a gate oxide layer or a field oxide layer). Usually, the field electrode and also the insulation layer enclosing the field electrode completely fill the lower part of the trench. The vertical extent of the field electrode is preferably configured such that it essentially corresponds to the vertical extents of the drift regions provided in the adjacent mesa regions.
The field electrode serves to provide, in the off state of the field plate trench transistor, countercharges with respect to the ionized dopant atoms in the drift zones, which are localized in the adjoining mesa regions. The provision of the countercharges brings about a depletion of charge carriers in the drift zones and thus an improvement in the blocking capability of the field plate trench transistor in the off state. The gate electrode in the upper part of the trench serves to form channels in the body regions, i.e. to switch the transistor from an off state to an on state.
The blocking capability of the field plate trench transistor depends to a large extent on the thickness of the insulation layer for insulation of the field electrode in the lower region of the trench. The thickness of a field oxide layer for a 100 V blocking field plate trench transistor is typically 500 to 1500 nm. If the blocking capability is to be increased, then the field oxide has to be thickened. However, thickening the field oxide generally also results in widening of the gate electrode. Moreover, since the thickness of a gate oxide layer turns out to be significantly smaller than the thickness of the field oxide layer, the gate electrode enclosed by the gate oxide layer takes up a very large volume (the entire free space enclosed by the gate oxide layer is usually filled with gate electrode material).